Transmissions featuring floating transmission mainshaft gears such as associated with twin countershaft transmission are well known and examples of which can be found in U.S. Pat. Nos. 3,237,472; 3,238,613; 3,425,290; and 3,885,446, the disclosures of which are incorporated herein by reference.
Such transmissions generally feature a plurality of floating mainshaft gears that encircle the mainshaft and are supported and driven by countershaft gears, typically two countershaft gears, that are mounted on a pair of countershafts disposed on opposite sides of the mainshaft.
The mainshaft gears are characteristically clutched to the mainshaft by means of a clutch mechanism that slides along external splines extending axially along the mainshaft and has radially inwardly extending teeth or splines that engage internal teeth or splines on the mainshaft gear so as to cause rotation of the mainshaft when the mainshaft gear is clutched thereto.
A problem long ago recognized has been the potential for transfer of axial thrust to a floating mainshaft gear being clutched to a mainshaft by an axially moving clutch assembly. In view of such, a variety of solutions have been devised over past years for transmitting axial thrust to the mainshaft that has been imparted to a mainshaft gear by an axially moving clutch assembly rather than a mainshaft gear adjacent the gear being clutched to the mainshaft.
Such solutions have generally been in the form of gear retainer(s) of one type of another that characteristically limit axial movement of the mainshaft gears to prevent them from engaging each other whether or not one of them is being clutched to the mainshaft.
One example of a retainer assembly for limiting axial movement of a transmission gear is disclosed in U.S. Pat. No. 2,397,905, the disclosure of which is incorporated herein by reference. Here however, a costly and expensive pivotal woodruff key is required to lock a thrust collar onto external splines of the mainshaft to prevent a gear from moving axially.
An example of a splined thrust washer for transmitting axial thrust from a gear set to a propeller drive shaft is disclosed in U.S. Pat. No. 3,894,621, the disclosure of which is incorporated herein by reference. Here, a splined thrust washer (52) is slid along the shaft splines to a transverse groove adjacent a stepped shoulder on the shaft and is held in place against the shoulder by a splined collar (30). Thrust washer (52) is operative to transmit axial thrust of only one gear to the propeller shaft and in addition to requiring the use of Collar (30), also requires costly and complex machining of a stepped configuration to the Propeller shaft exterior.
A more recent example of a transmission mainshaft gear retainer for preventing axial movement of two closely spaced gears to prevent transfer of axial thrust force therebetween is disclosed in U.S. Pat. No. 4,034,620, the disclosure of which is incorporated herein by reference. Here a thrust ring (104) is splined to the mainshaft between two adjacent gears and is held in place by means of snap rings (108, 110) on opposite sides thereof. The gears are further required to have costly and complex mating tongue and groove configurations that operate in conjunction with an additional snap ring (102) to limit movement of the gears away from each other.
An even more recent example of a three thrust washer combination for transmitting axial thrust imparted to a mainshaft gear to the mainshaft and upon which the present improvement is founded is disclosed in U.S. Pat. No. 4,949,589, assigned to the assignee of the present invention and the disclosure of which is incorporated herein by reference. Here, however, all three washers require relatively large width transverse grooves for their axial containment in the outer surface of the mainshaft as well as requiring that all three be secured for rotation with the mainshaft by a conventional prior art key that extends axially along one of the grooves in the mainshaft splines and into the clutch engagement region and thus requiring the removal of one of the clutch assembly teeth to enable the clutch assembly to slide axially over the key.
In contrast to the above, the present invention requires only one relatively wide width groove in combination with two narrow width grooves for containing a three thrust washer combination coaxially as well as requiring that only the middle thrust washer of the three thrust washers be secured to the mainshaft by a key and thus eliminating the requirement that a tooth be removed from the clutch assembly whereas the thrust washers respectively located on opposite sides of the middle thrust washer are able to utilize splines on the mainshaft for their respective securement and rotation therewith and are prevented from moving axially away from each other by retaining rings disposed inthe narrower width transverse grooves in the outer surface of the mainshaft.